Variable tuning arrangement



6 l a n m e AM 4% 2 a ma Am M vi m I S I M Aug. 1% W49.

Flled 0m 21., 1947 16419490 I. J. KAAR 2,4793% VARIABLE TUNING ARRANGEMENT Filed Oct. 21, 1947 2 Sheets-Sheet 2,

Inventer: Ira J. Kaar 9 bym 2% His Attor-mey- Patented Aug. 16, 1949 VARIABLE TUNING ARRANGEMENT Ira J. Kaar, Baldwinsville, N. Y., assignor to General Electric Company, a corporation of New York Application October 21, 1947, Serial No. 781,034

2 Claims. 1

My invention relates to variable timing arrangements for radio receivers and similar apparatus, and more particularly, to a variable tuning arrangement for the signal input and converter-oscillator circuits of a superheterodyne receiver. It is a primary object of my invention to provide a compact arrangement of this type obtaining improved performance characteristics of such a receiver.

It is a customary practice in superheterodyne receiver design to employ a loop antenna in conjunction with a variable capacitor as a selective signal pickup device. The local oscillator may be tuned either by a variable capacitance or by one or more variable inductances. A capacitance-tuned local oscillator, however, has a tendency to produce a howl or squeal in the output circuit of the receiver, due to the susceptibility of the capacitor vanes to vibration. It has been found that the use of an inductancetuned local oscillator results in a reduction of the howl tendencies of the receiver. It has also been found advantageous to use a capacitance to tune the loop circuit of a receiver for reasons of enhanced sensitivity. Hence, it is desirable to employ a variable tuning arrangement comprising a variable capacitor element, for tuning the loop circuit, which operates simultaneously with one or more variable inductor elements, for tuning the local oscillator circuit, in such a way as to effect perfect tracking. It is a particular object of my invention to provide such a variable tuning arrangement.

Another object of my invention is to provide means of simultaneously tuning a capacitor in one circuit and a plurality of inductors in one or more associated circuits in such a way that the respective frequencies of the circuits involved maintain a predetermined relationship to each other throughout the tuning range.

A further object ofmy invention is to provide reliable and convenient means for setting up and maintaining the desired tracking relationship between the associated circuits at reduced cost.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a side elevation, partly in transverse section, of a variable tuning arrangement suitably embodying my invention; Fig. 2 is a partial plan view of the same arrangement; Fig.

3 is a partial plan view of another modification;

and Fig. 4 is a schematic circuit diagram illustrating an application of my invention to a superheterodyne radio receiver.

Referring to Fig. 1, a die-cast metal supporting member 1, preferably of aluminum or other light conducting material, is provided integrally with a protruding truncated cone-like structure 2 which constitutes the stator or stationary element of a variable capacitor. The stator 2 is provided with an axial recess 3, also shaped like a truncated cone, but inverted with respect to the outer structure 2. Also die-cast as integral parts of the supporting member I are two coil form support bushings 4 and two guide rod support bushings 5. One or more coils 8 having suitable inductance characteristics are mounted on respective hollow coil forms I of suitable insulating material which are rigidly inserted and fixed in each of the support bushings 4. Illustrations of the connection terminals for the coils 6 are omitted in order to simplify the drawing. The support bushings 5 are provided with round metal guide rods 8 which are rigidly attached therein. The supporting member I is also provided with mounting holes 9 by which means supporting member I is maintained in a. fixed position relative to the chassis.

A substantially cylindrical structure [0 is provided having a hollowed-out annular recess ll of such shape as to permit structure In to mate axially with the stator 2. This structure I0 is die-cast of the same material as the stator 2 and constitutes the rotor of the aforementioned variable capacitor. I also provide a second diecast supporting member l2, having a centrally located hole l3, and comprising as integral parts thereof a pair of elongated guide rod bushings l4, so positioned that when the guide rods 8 are inserted therein, the hole l3 in member I2 is in substantially coaxial alignment with the stator 2. The bushings I4 are so proportioned as to fit the guide rods 8 as snugly as possible consist: ent with allowing longitudinal motion thereon.

In order to insure perfect axial alignment between the stator 2 and the rotor Ill, means are employed for laterally adjustably fastening the rotor In to the second supporting member [2. Such means as shown take the form of a threaded stud l5, of smaller diameter than hole iii in member l2, permanently fastened to the rotor H]. An adjusting nut It then fastens the rotor In to member l2; the customary washer I1 is provided. In order to center the rotor In, the adjusting nut I6 is loosened and the entire an signal input frequencies to the tuned;

ment of the rotor l-fl with the stator '2.

relative to the rotor ID of the variable. capacitor,

and thus effects an initial tracking relation between the associated circuits. Lock nuts"?! are supplied to secure the positions of the cores l9 relative to *the motor =19 aster rnal'eing the initial traelr ing-*-ad=iustments. a I

' IlikeW-ise, means are *previded for moving the supportingmember's 'i a'snd t? withrespeotato each other-so that a sin'glepperating shaft. 22 Lbe used to obtain simultaneous adjustment :of inductance and capacitanee. means are shown comprising 'a yoke 23 fastened to-niembel W and straddling the adjusting nut iii Ivtemb'ers I and ll are relatively position-ed by rotation of theoperating shafte21 Fig. *2 isa qs-aiItialfpla'n viewof the shown in Fig. l which, taken :in connection with Fig. I, defines more exactly the shapes of the rotor I-B- th'e stator 2 f v 'ble condenser. =Fig. "3*shows a modification of my inventfon' in that three tunable oeil-s 8 are provided instea'doftwo, as in lan'd Iiikemefew ence numerals indicate-similar elements :in Figs I, 2'and 3. 1

In the circuitm-f Fig. 4,-a liigh=-vacuum pentode 3 *or' other sui-table electron dischar'ge device, is employed as a =re'dio.-free ueney amp er :a :su perh'eterodyne -receiver. The signal input grid seer device 3: reconnectedtozasignalinput cir- 1 windingof a singly-tuned radio f Q former fie' to =theiiirect plate sup-ply Volta ge, indicated by the ile'genii 13+ screen i electrode -89 of "device M is "connected directly to B iriduotance eapaeit'ance network comprising "the primary er the radio frequency "trainner ii? and a conpli n-gcapacitor fi-l passes sub. "anti-ally ircn'it i2, is wvellknown in the art. Tuned oircdit A2 comprises the-sebcndaryfl of thera'dio irequen'cy transformer 5!], which is tuned by means of ain adiiustable iron -"core-, set shown. 'a par lel eapaeitanoe fi i, and is provided with the usual m immei conden'ser i 'fi.

A hi'g h vaouum heptode 68 is employed as a oonvert'er oscillator device, the oscillator anode,

grid and c'athode elements of Which are located at; 41;, 8, 41!! respectively. The local oscillator isiineluctanceetnned by ililBEtlZl-Sbfifill'liUSCllifiliOIiCQll 50 shrmted by a trimming ciondens'erfi I. Thissinductan'ce of *coi'l fifluis variable-over a suitable-Lop .oratm wrfan gesby-imeans of a conventionallpowdered iron core (not shown) and comprises one of the variable inductances heretofore described.

ihe amplified radio frequency signal is supplied, through the radio frequency transformer 49, to the mixer grid 52 of device 46. The output of device 46 is connected through the customary intermediate frequency transformer 53, to an intermediate frequency amplifier tnot. -shown). Furtherdescription of the circuits-of thereceiver and elements thereof is believed to be unnecessary, since the circuit shown illustrates a present preferred use ilor my invention.

In the circuit of Fig. 4, my variable tuning arrangemeHt-A-is used-to'tune conjointly the antenna,

-radiofrequency,"and local oscillator stages of a superheterodyne receiver, the tuning elements being mechanically connected as indicated for unicontrol operation, and comprising the variable capacitor and the tunable coils 6 of Fig. 1. In some cases, the trimming condensers 45, Si may be eliminated, 'ithus "obtaining economy of parts, the tracking relationship dieing reflected entirely by positioning .the-ziron'cores. t9 with-11espsct 3151), the rotor tit of the 'variahleeapacitor.

fifhe.vaniableieapacitnr showin sheets-linear .cas pacitance tuning; therefioraior perfect tracking, linearly 'irolnable. inductances. .aa'e; areduired. Such linear :itnrnng in the rradiodrequency andillocal oscillator circuits ma be obtained shyamaking the cciisafi 6Fig...=];) .of variablepit'ch,orhyother snitableimeans.

.Ailthough my invention :has -=been described .in itszpresent preferred application to the tuning system ofza.superheterodyne; receiver, itrisxzunder stood that various modifications. :may be made. The appended ClELi'HlS. are intended @to cover all equivalent modifications. coming within the $1119 spirit and scope. whiny invention.

What '13 claim as; new rand-desire its secure lay Letters Patent of the, United States is:

'1. .ln'oombination pair oiiiuxtaposedmetailic memberssoneiof -s aidsmembers aliasing an integral truncated COBB-Shflffidlgl'iflflltififl towzurd the other .=n1e1riber,,.said portion hatzinew trally position-ed truncated cone-shaped recess, a. 'ci/vlimdrical stiiucture. laterally iadjustably' :Eas- EEllE'd'fitD saidiotherimernber' rtnwnrd said orrennember saidstructure :haviez aan larreeesshaxiingxwallsparallelmespeotiuely t "the wallsoisaid portion; andr-s'aidrconeeshnped a of :brtslnngs iintegaralw n said-other member with mores-having axes parallel "ith the a of rotation of said annulnrmeccss,iaipairmfguide rods-s rigidly connected to. said one. :member and respen'tine'ly engaging difienent :of :said bs-res, said randfhushingsziheing so :rrositioncdthat :axes of said structure and-said:portion are coincidentralpztir of 'tubularzeoil or ls'supporte'd on first. of: said members, wind gs'positioned on said forms, -.a ipai'r Uf magneitic cores adjustably' sill porte'don the second of members, said scores respectively :being to enter intozriifierent air-said for-"ms, :said forms said cores havin g El'ong-itudina-l axes parallel With said ent axes, tl 're axes or corresponding 0: said ionms' and cores being coincident, saidportion and said structure forming an electrical capacitance, and :means wherby th-e relative positions of said por 'tion andsaid'structure may be varied .along=their said axes to the value of ='capaci tance and the inductance of said wh ings.

:2. :a radio receiver having- =a plurality of resonantircircuits tunaibi-eover a band of frequencies, ronewf'said circuits comprising a van 5 able capacitance and a pair of said circuits comprising variable inductances, said variable capacitance comprising a. pair of rotationally symmetrical mating members having coincident axes, one of said members having a truncated coneshaped outer surface and a centrally positioned truncated cone-shaped recess, a structure having an annular recess laterally adjustably fastened to the other of said members, a respective base portion attached to each of said members, a pair of guide rods attached to the base portion of a first of said members and extending parallel to said axes, a pair of bushings integrally attached to the second of said members and having bores adapted to engage said rods, said inductances comprising a pair of windings supported from the base portion of one of said members and a pair of substantially cylindrical iron cores supported from the base portion of the other of said members, said cores respectively being arranged to enter into different of said windings, the position of one of said cores being adjustable relative to the base portion of said other member to adjust the inductance of the windings associated therewith, and means whereby the positions of said members may be varied along said coincident axes to adjust the value of said capacitance and the inductance of said windings.

I IRA J. KAAR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,772,839 McIver Aug. 12, 1930 1,945,584 Deutscher Feb. 20, 1934 2,199,669 Laughlin May 7, 1940 Sands et a1 Jan. 4, 1944 

